by neufer » Mon Sep 19, 2016 6:22 pm
Boomer12k wrote:Michael B. Luskin wrote:
When we talk about the "surface" of a star, or, for that matter, a gaseous planet what do we mean?
The top layer we generally see....we call that the "surface"... it isn't a matter of the material, but generally some "hard part" as opposed to a Gas. It is the apparent top...
sometimes....like "the surface of the ocean"... or "the surface of that table"...Now with Earth, or Mars, or Venus, or a Moon, we mean the top hard rocky layer of land , water is said to cover the surface...and we don't mean the atmosphere. But I did say..."generally"... With a planet like Jupiter, it could get dicey... it does not seemingly have a solid surface. The Sun HAS a surface. It is a calcium ferrite surface layer...and is "rocky"...The photosphere is above that and is a plasma, an "atmosphere" and so covers the actual "surface of the Sun", like water.... look up... the surface of the Sun...
For a gaseous planet, a revolving oblate spheroid set at the point at which atmospheric pressure equals 1,000 mb (i.e., 100 kPa) is conditionally designated as the planetary "surface."
For stars (including the Sun) the surface is defined as "the edge" of the photosphere (where the optical depth ~ 2/3). The gas pressure the Sun's "surface" is only ~10 mb (i.e., ~1 kPa).
https://en.wikipedia.org/wiki/Sun#Photosphere wrote:
<<The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately 2/3. In other words, a photosphere is the deepest region of a luminous object, usually a star, that is transparent to photons of certain wavelengths.
The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light. Above the photosphere visible sunlight is free to propagate into space, and its energy escapes the Sun entirely. The change in opacity is due to the decreasing amount of H
− ions, which absorb visible light easily. Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H
− ions.
The photosphere is tens to hundreds of kilometers thick, and is slightly less opaque than air on Earth. Because the upper part of the photosphere is cooler than the lower part, an image of the Sun appears brighter in the center than on the edge or limb of the solar disk, in a phenomenon known as limb darkening. The spectrum of sunlight has approximately the spectrum of a black-body radiating at about 6,000 K, interspersed with atomic absorption lines from the tenuous layers above the photosphere. The photosphere is not fully ionized—the extent of ionization is about 3%, leaving almost all of the hydrogen in atomic form.>>
https://en.wikipedia.org/wiki/Hydrogen_anion wrote:
The hydrogen anion is a negative ion of hydrogen, H
−. The hydrogen anion is an important constituent of the atmosphere of stars, such as the Sun. The ion has two electrons bound by the electromagnetic force to a nucleus containing one proton. The hydrogen anion is an important species in the photosphere of the Sun. It absorbs energies in the range 0.75–4.0 eV, which ranges from the infrared into the visible spectrum (Rau 1999, Srinivasan 1999). It also occurs in the Earth's ionosphere (Rau 1999). Its existence was first proven theoretically by Hans Bethe in 1929 (Bethe 1929). H
− is unusual because, in its free form, it has no bound excited states, as was finally proven in 1977 (Hill 1977).>>
[quote="Boomer12k"][quote="Michael B. Luskin"]
When we talk about the "surface" of a star, or, for that matter, a gaseous planet what do we mean?[/quote]
The top layer we generally see....we call that the "surface"... it isn't a matter of the material, but generally some "hard part" as opposed to a Gas. It is the apparent top... [u]sometimes[/u]....like "the surface of the ocean"... or "the surface of that table"...Now with Earth, or Mars, or Venus, or a Moon, we mean the top hard rocky layer of land , water is said to cover the surface...and we don't mean the atmosphere. But I did say..."generally"... With a planet like Jupiter, it could get dicey... it does not seemingly have a solid surface. The Sun HAS a surface. It is a calcium ferrite surface layer...and is "rocky"...The photosphere is above that and is a plasma, an "atmosphere" and so covers the actual "surface of the Sun", like water.... look up... the surface of the Sun...[/quote]
For a gaseous planet, a revolving oblate spheroid set at the point at which atmospheric pressure equals 1,000 mb (i.e., 100 kPa) is conditionally designated as the planetary "surface."
For stars (including the Sun) the surface is defined as "the edge" of the photosphere (where the optical depth ~ 2/3). The gas pressure the Sun's "surface" is only ~10 mb (i.e., ~1 kPa).
[quote=" https://en.wikipedia.org/wiki/Sun#Photosphere"]
<<The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately 2/3. In other words, a photosphere is the deepest region of a luminous object, usually a star, that is transparent to photons of certain wavelengths.
The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light. Above the photosphere visible sunlight is free to propagate into space, and its energy escapes the Sun entirely. The change in opacity is due to the decreasing amount of H[sup]−[/sup] ions, which absorb visible light easily. Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H[sup]−[/sup] ions. [b][color=#0000FF]The photosphere is tens to hundreds of kilometers thick, and is slightly less opaque than air on Earth[/color][/b]. Because the upper part of the photosphere is cooler than the lower part, an image of the Sun appears brighter in the center than on the edge or limb of the solar disk, in a phenomenon known as limb darkening. The spectrum of sunlight has approximately the spectrum of a black-body radiating at about 6,000 K, interspersed with atomic absorption lines from the tenuous layers above the photosphere. The photosphere is not fully ionized—the extent of ionization is about 3%, leaving almost all of the hydrogen in atomic form.>>[/quote][quote=" https://en.wikipedia.org/wiki/Hydrogen_anion"]
The hydrogen anion is a negative ion of hydrogen, H[sup]−[/sup]. The hydrogen anion is an important constituent of the atmosphere of stars, such as the Sun. The ion has two electrons bound by the electromagnetic force to a nucleus containing one proton. The hydrogen anion is an important species in the photosphere of the Sun. It absorbs energies in the range 0.75–4.0 eV, which ranges from the infrared into the visible spectrum (Rau 1999, Srinivasan 1999). It also occurs in the Earth's ionosphere (Rau 1999). Its existence was first proven theoretically by Hans Bethe in 1929 (Bethe 1929). H[sup]−[/sup] is unusual because, in its free form, it has no bound excited states, as was finally proven in 1977 (Hill 1977).>>[/quote]